Ample evidence supports the assertion that the latency of the P300 component of the human event-related brain potential is proportional to stimulus evaluation and categorization processes and is relatively independent of response selection and execution processes. We shall use P300 latency to gain a more detailed understanding of the ubiquitous slowness of behavior in the aged. This project will be conducted in collaboration with Rush-Presbyterian-ST. Luke's Medical Center in Chicago. Such collaboration will bring together the necessary skills as well as the required subject population in which to develop a battery of psychophysiological tests in which P300 latency can be dissociated from reaction time. Each of these tests will assess the duration of a specific phase or stage of huma information processing. The tests will be administered to young adults in Champaign-Urbana and to the "normal control group" of aged individuals in the "normal controals" assembled in the Program Project "Cerebral Decline in Aging" (3P0-AG-00905) at Rush-Presbyterian Medical School in Chicago. The results should allow us to determine which, if any, of the several stages of information processingis specifically affected by aging.